1. Field of the Invention
This invention relates to improvements in a vertical magnetic recording medium used for a vertical magnetic recording.
2. Description of the Prior Art
Heretofore, there is known a vertical magnetic recording medium used for a vertical magnetic recording, in which a vertically magnetized film made of a thin alloy film containing Co and Cr as main ingredients is provided on a nonmagnetic substrate. The thin alloy film which contains Co-Cr as main ingredients has a hexagonal close-packed structure as its crystal structure to generate a vertical magnetic anisotropy in such a manner that its C axis is oriented vertically to the surface of the film. It is to be noted that in order to form a preferably vertical magnetic recording medium, its C-axis orientation must be excellent. It is known that, for forming such a medium, a 2-layer medium having a Permalloy.RTM. film provided between nonmagnetic substrate and a vertically magnetized film improves its reproduction output as compared with a structure having no Permalloy.RTM. film. The Permalloy.RTM. film displays magnetic saturation at a high level such as 10,000 gauss and displays large specific permeability such as approx. 3,000, and is optimum as a soft magnetic layer of a 2-layer medium. However, the crystal orientation of the Permalloy.RTM. film on the nonmagnetic substrate is not conducive enough for high efficiency, and it is difficult to obtain a preferred high degree of crystal orientation with the vertically magnetized film form thereon owing to the influence of the crystal orientation of the Permalloy.RTM. film. A relatively thick film (approx. 1,000 nm) is required as compared with the recording layer as the Permalloy.RTM.. Even though a Permalloy.RTM. structure manufactured by a plating method and having a large thickness can be simply obtained with high productivity, its crystal orientation is significantly unfavorable. Available prior art teaches several arrangements directed to improve the orientation property of a combination of a Permalloy.RTM. film and a Co-Cr film.
In order to control the deterioration of the crystal orientation of the vertically magnetized film formed on a soft base layer made of Permalloy.RTM., a vertical magnetic recording medium is heretofore proposed, as disclosed in Japanese Patent Laid-open Sho 59-75429 official gazette, in which a Ti film is provided between a soft base layer and a vertically magnetized film to improve the crystal orientation of the vertically magnetized film by utilizing the crystal orientation of the Ti film. There is also proposed, as disclosed in Japanese Patent Laid -open Sho 57-208630 official gazette, a vertical magnetic recording medium in which a nonmagnetic and amorphous layer made of SiO.sub.2 or Al.sub.2 O.sub.3 film is provided as an intermediate layer between a soft base layer and a vertically magnetized film to similarly improve the crystal orientation of the vertically magnetized film. Further, there is also proposed, as disclosed in Japanese Patent Laid-open Sho 61-267927 official gazette, a vertical magnetic recording medium in which a soft magnetic amorphous film made of Co-Zr-Mo is used as an intermediate layer.
However, since the intermediate layer is nonmagnetic in the conventional vertical magnetic recording medium using the above-described Ti, SiO.sub.2 or Al.sub.2 O.sub.3 film as the intermediate layer, the magnetic coupling of the vertically magnetized film to the soft base layer is not so effective, with the result that the improvement in its recording efficiency is still insufficient. Further, even in case of the vertical magnetic recording medium which has the amorphous soft magnetic Co-Zr-Mo layer as the intermediate layer, its orientation is not as desired.
An object of the present invention is to provide a vertical magnetic recording medium and a method of manufacturing the same which can obviate the problems of the above-described prior art.